The ever increasing amount of air traffic has caused a marked increased in the workload of air traffic control (“ATC”) controllers in high traffic density areas around airports. The Next Generation (NextGen) overhaul of the United States airspace system and the companion Single European Sky ATM Research (SESAR) overhaul of the European airspace system are proposing various trajectory-based mechanisms to ease the pressures on the air traffic management. Some solutions being suggested include the increased use of onboard Required Time of Arrival (“RTA”) systems that allow an aircrew limited control of aircraft spacing and separation in areas where ATC personnel may face heavy work loads.
These RTA systems may also be used to control speed transitions in multi-segment flight plans. Flight plans are developed in segments between “waypoints” or points in space defined by latitude, longitude, an altitude. These segments have physical or regulatory maximum and minimum airspeed constraints. Further, one or more waypoints in the flight plan may have a required time of arrival (“RTA”) assigned to those waypoints which may be a specific arrival time (i.e. a “hard RTA”) or may be a one sided restriction such as arriving “no earlier than” or “no later than” a specific time. The principles described herein are applicable to flight plan scenarios comprising multiple speed segments to a waypoint with an RTA, or between two waypoints with hard RTA's where passing the first hard RTA commences the scenario.
However, there are uncertainties involved in traversing an RTA generated flight plan trajectory. These uncertainties may include ATC restrictions/clearances, wind changes and unexpected weather, among others. Therefore, when developing a flight plan, flight planners avoid altitudes and speeds that approach regulatory, operational or physical airframe limitations, particularly when approaching an RTA waypoint. It is prudent to operate an aircraft in a way that permits ample maneuvering flexibility so that the RTA can be met. Hence, flight planners build in adequate leeway or “pad” their flight plans such that an aircraft has reasonable room to accelerate/decelerate or to climb/descend if the need or opportunity arises. This may be done by building in air speeds that are materially lower than either the maximum recommended speed tolerance of the airframe/engines or below the ATC imposed speed limits, whichever is lower. The difference between the planned air speed and the maximum (or minimum) allowable air speed in a segment of a flight plan will be referred to herein below as the segment control margin or the “pad” of the segment.
Flight planners are particularly concerned about conserving the pad of later and/or speed constrained flight plan regions particularly when these regions immediately precede a RTA waypoint with its specified time requirements. Planners want to have some speed maneuverability as the RTA waypoint is approached so that the RTA can be met smoothly without excessively changing speed.
Similarly, the region immediately preceding an RTA waypoint may become physically constrained due to the physically impossibility of meeting an RTA if the aircraft falls too far behind schedule. Flight planners want to conserve the pad in a speed constrained region should it become necessary to accelerate while traversing speed constrained segments to meet an RTA and not violate speed constraints.
If the aircraft does fall behind the flight plan in a particular region, the aircraft may increase speed (e.g., consume the pad) in its current segment until the aircraft is again able to meet the RTA at the waypoint of concern by adhering to the remainder of the flight plan. It may or may not be possible to increase speed sufficiently in the aircraft's current segment to meet the RTA. In any event, it is also fuel inefficient to accelerate from a planned air speed in one segment to reach a waypoint on time to then slow back down to a planned air speed of the next segment when the aircraft enters the next segment just to again accelerate when the aircraft falls behind the RTA because the flight uncertainties persist.
Accordingly, it is desirable to develop a system and method to compensate for experience flight uncertainties while traversing earlier flight segments. In addition, it is desirable to adjust the aircraft speed profile in multiple segments simultaneously. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.